Scan2CAD raster to vector conversion software

REVIEW:

Graphtec CSX300 large format scanner

... Continued. [Graphtec CSX300 - previous] [Graphtec CSX300 - next]

Scanning in Greyscale

CAD users will not normally need to scan in greyscale, however we include greyscale in this review because the CSX300's greyscale scanning illustrates an interesting technical detail about scanners.

Scanners like the CSX300 that use CIS imaging technology use red, green and blue LED illumination. To scan in colour, they scan each scan line using the red LED, then the green LED, then the blue LED. They then collate the data from the three colours to produce the colour image. To scan in black and white or greyscale, they either scan each scan line using the red, green and blue LEDs simultaneously (RGB) or they scan using just the green LED (greenscale).

Whether a scanner scans monochrome using RGB or in greenscale makes no difference until you try to scan a colour image in greyscale or black and white. If the scanner is using RGB you will get a greyscale scan that agrees with the human perception of how the colour image should look in greyscale. If the scanner is using green only, some colours will appear incorrect. This in turn will affect the way the image is thresholded to black and white.

By default, the CSX300 scans in greenscale. However, Scanning Master includes a Gray Balance option and when this is selected, the CSX300 scans with RGB. This makes it an ideal scanner on which to test the differences between greenscale and RGB scanning!

For example, consider the following colour photograph:

Here is the photograph scanned using the CSX300's default greenscale (left) and using the RGB Gray Balance option (right):

You can see that in the greenscale picture, the red and dark green threads are undifferentiated whereas in the RGB one, the red thread is shown in a lighter shade of grey, which is more how you would expect it.

If you now threshold the greyscale images to black and white, the results are quite different:

[Graphtec CSX300 - previous] [Graphtec CSX300 - next]